In one manufacturing method, a broaching tool is produced from tool steel bar stock by first turning the bar in the soft condition (annealed condition) in a manual lathe operation to form the puller portion adjacent one end of the bar, the retriever portion adjacent the other end and the toothed cutting portion, including a roughing section, semi-finishing section and finishing section, intermediate the puller and retriever portions. Each cutting section includes sequentially arranged cutting teeth having a uniform cutting edge and predetermined increase in tooth size along the length of the cutting portion. In the manual lathe operation, the puller portion, retriever portion and toothed cutting portion are machined to within 0.030-0.050 inch of finished dimension. The so-called gullet radius and hook angle of the cutting teeth are turned in true relation with each other in the manual lathe operation.
Thereafter, the rough turned broaching tool is heat treated to a hardness of R.sub.c 65 and the cutting edges of the teeth are brought up sharp from the gullet radius manually using a broach sharpening machine designed specifically for this purpose. Then, the external diameters of the broach teeth are reduced to finish size by an O.D. grinding operation with each tooth ground one at a time. The total manufacturing time for a typical round broach employing these steps has been on the order of 8-9 hours and is very manual labor intensive.
The Grace U.S. Pat. No. 4,498,361 issued Feb. 12, 1985, describes an improved method for manufacturing a broaching tool wherein bar stock in the soft or unheat-treated condition is turned to rough machine the outer diameter of the puller and retriever portion and the cutting portion to within 0.030-0.050 inch of finished dimensions. During this rough turning step, the broach teeth are turned to have a finished gullet cavity with the gullet radius intersecting an oversized hook angle on each tooth. Following heat treatment of the rough turned stock, a second turning operation is conducted in which the rough turned stock in the hard (heat treated) condition is turned to reduce the tooth outer diameters and to machine the back-off angles on the roughing section and semi-finishing section to finish dimension. The outer diameter and back-off angle of the finishing section is turned to slightly oversize dimension and then the hook angle "oversize" is nicked off and blended with the previously soft-turned gullet radius. After the hard turning operation, external diameters and back-off angles of the teeth in the finishing section may be subjected to a grinding operation to provide the close tolerances normally required in the finishing section of the cutting portion. The outer diameters of the finishing section are brought to finished dimension by performing a grinding operation on each tooth one at a time until all of the teeth have been ground to finished dimension.